Expandable Support Device and Method of Use

ABSTRACT

An implantable orthopedic support device and methods of using the device are disclosed. The device can have rigid structural components that can translate longitudinally with respect to each other, and in so doing can change the vertical height of the device. The structural components can be driven by a drivescrew mechanism to change the vertical height of the device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to andbenefit under 35 U.S.C. §120 to copending U.S. application Ser. No.13/870,584, filed Apr. 25, 2013, which claims priority to and benefitunder 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/638,148,filed Apr. 25, 2012, and U.S. Provisional Application No. 61/638,146,filed Apr. 25, 2012, the entire contents of which are herebyincorporated by reference.

BACKGROUND

1. Technical Field

Devices and methods for fixation of tissue are disclosed. Morespecifically, the devices and methods can be for interbody vertebralfusion of vertebrae or for fusion of other bones to one another.

2. Background of the Art

There already exist many intervertebral spacers of fixed dimensions.There are also some expandable intervertebral spacers, which allowinsertion through a relatively small surgical incision, followed byexpansion of the device once it is in position at the surgical site.However, there is still a need for improved expandable spacers.

SUMMARY OF THE INVENTION

Embodiments of the invention may generally comprise a central mechanismthat comprises a proximal ring structure and a distal ring structure.The proximal ring structure and the distal ring structure may be able totranslate relative to each other. At least one or both of the proximalring structure and the distal ring structure may comprise ramps. Rampsmay be any combination of interlocking and non-interlocking. Embodimentsof the invention may further comprise endplates, which may be able tomove vertically toward or away from each other in response to relativetranslational motion of the proximal ring structure and the distal ringstructure, and which may comprise ramps that are complementary to rampsin the ring structures.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which one of the ring structures hasfour sides, and of those four sides, two opposed sides have offsets suchthat there can be defined a first inside width and a second inside widthand a first outside width and a second outside width, wherein thesmaller of the outside widths is less than the larger of the insidewidths.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which at least one of the ringstructures has a central opening that has a first internal widthdimension and a second internal width dimension, wherein the firstinternal width dimension is different from the second internal widthdimension.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which the proximal ring structure has afirst ramp and a second ramp, in which the first ramp comprises areceiving structure capable of engaging a first complementary shape, andthe second ramp comprises a protruding shape capable of engaging asecond complementary shape.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which the proximal ring structure has afirst ramp that extends continuously across the centerplane, and inwhich the proximal ring structure also has two additional ramps, one oneach side of the centerplane, and not intersecting the centerplane, withthe two additional ramps being coplanar with each other.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which the proximal ring structure has aplurality of ramps, in which at least one of the ramps has an engagementfeature and another of the ramps does not have an engagement feature. Anengagement feature may be either a protrusion or a receiver, and may beeither interlocking or non-interlocking.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which the proximal ring structure has athree different outward-facing ramp surfaces, in which the threedifferent outward-facing ramp surfaces are parallel with each other butare located in three different non-coplanar planes.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, in which the proximal ring structure has aplurality of outward-facing ramps, such that each ramp has a respectiveramp width, measured in a lateral direction, of whatever portion of theramp surface is planar, wherein the widths of different ramps areunequal.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the distal ring structure comprisesa vertically extending urging structure and a transition between theurging structure and the distal ring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the distal ring structure has asmallest internal width in a lateral direction and has a verticallyextending urging structure having an urging structure width in a lateraldirection, wherein the urging structure width is less than the smallestinternal width of the distal ring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the proximal ring structure and adistal ring structure, when viewed along a vertical direction, partiallybut not completely overlap with each other.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein at some place the proximal ringstructure has an external lateral dimension smaller than a correspondinginternal lateral dimension of the distal ring structure, and in anotherplace, the distal ring structure has an external lateral dimensionsmaller than a corresponding internal lateral dimension of the proximalring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein, in all permitted positions of thedistal ring structure relative to the proximal ring structure, in asection of the device taken along a longitudinal direction, there is afirst end of the proximal ring structure, followed by a first end of thedistal ring structure, followed by a second end of the proximal ringstructure, followed by a second end of the distal ring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein, in some cross-section taken in afirst plane perpendicular to a longitudinal direction, there is insequence progressing in a lateral direction the proximal ring structurefollowed by the distal ring structure followed by some empty spacefollowed by the distal ring structure followed by the proximal ringstructure, and wherein, in some other cross-section taken in a secondplane perpendicular to the longitudinal direction, there is in sequenceprogressing in a lateral direction, the distal ring structure followedby the proximal ring structure followed by some empty space followed bythe proximal ring structure followed by the distal ring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the device has a central openingtherethrough generally along a vertical direction, and wherein thecentral opening is bounded in sequence around its perimeter by a firstend, a first side, a second end and a second side, wherein in thesequence, is bounded on the first end by the proximal ring structure;then, on the first side adjacent to the first end, is bounded first bythe proximal ring structure and then by the distal ring structure; then,on the second end is bounded by the distal ring structure; then, on thesecond side, is bounded first by the distal ring structure and then bythe proximal ring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatehas a central hole through the outward-facing surface and generallythrough the endplate, and wherein the central opening has a dimension ina lateral direction and the endplate has a pair of stability barsdepending therefrom away from the outward-facing surface, the stabilitybars having parallel surfaces facing toward each other defining adistance therebetween in the lateral direction, and wherein the distancebetween the stability bars equals the central hole lateral dimension.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatecomprises a first ramp comprising a protruding structure capable ofengaging a first complementary shape, and comprises a second rampcomprising a receiving shape capable of engaging a second complementaryshape.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatecomprises a first outward-facing ramp straddling both sides of acenterplane of the endplate, and further comprises further comprises adistinct separate outward-facing side ramp located so as not tointersect the centerplane of the endplate.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatecomprises a first outward-facing ramp surface that has an engagementfeature and a second outward-facing ramp surface that does not have anengagement feature. An engagement feature may be either a protrusion ora receiver, and may be either interlocking or non-interlocking.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatecomprises a first outward-facing ramp surface and a secondoutward-facing ramp surface and a third outward-facing ramp surface,wherein the first, second and third outward-facing ramp surfaces lie indifferent planes and are parallel to each other.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatecomprises a first outward-facing ramp surface and a secondoutward-facing ramp surface, wherein the first and second ramp surfacesare of unequal widths.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism and an endplate, wherein the endplatecomprises a ramp surface and also has a central hole therethrough,wherein the ramp intersects an edge of the central hole.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, and comprising an endplate, wherein theendplate comprises stability bar depending therefrom, wherein thestability bars are inside the proximal ring structure and inside thedistal ring structure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the distal ring structure has avertically extending urging structure having an urging structure widthin a lateral direction, and an endplate that is engaged with but movablewith respect to the central mechanism, the endplate having a centralhole having a central hole width in a lateral direction, wherein theurging structure width is less than the central hole width.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, and comprising an endplate having a centralhole therethrough and having a stability bar depending from theendplate, wherein the distal ring structure has an urging structure,wherein, in a longitudinal direction, the urging structure fits betweenthe central hole internal wall and the stability bar.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, and comprising an endplate, wherein theendplate has a pair of stability bars depending therefrom away from theoutward-facing surface and has a pair of overhanging guides dependingtherefrom away from the outward-facing surface, and wherein theoverhanging guides are more laterally outward than the stability bars.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a first structure and asecond structure, and comprising an endplate, having a central holetherethrough having an internal perimeter surface, wherein, in at leastone direction of motion, the urging structure bears against the internalperimeter surface of the central opening of the endplate.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a first structure and asecond structure, and comprising an endplate, having a central holetherethrough having an internal perimeter surface, wherein, in at leastone direction of motion, the urging surface bears against an externalsurface of the stability bar of the endplate.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a first structure and asecond structure able to undergo relative translation with respect toeach other, with at least one of the structures having a driving ramphaving an interlocking feature, and comprising an endplate having anendplate ramp complementary to the driving ramp and to its interlockingfeature, and comprising a drive means, wherein translation of thecentral mechanism in one direction drives the endplate away from thecentral mechanism and translation of the central mechanism in theopposite direction drives the endplate toward the central mechanism, andwherein the central mechanism has a central opening therethrough and thedrive means does not cross the central opening.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, and wherein the relative motion of theendplate relative to the proximal ring structure may be caused by anurging structure of the distal ring structure pushing on the endplateclose to a first ramp, and relative motion of the endplate relative tothe proximal ring structure may also or alternatively be caused by asurface of a distally located portion of the distal ring structurepushing on a distal surface of the endplate.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the proximal ring structure and thedistal ring structure are connected by a guide means and also by a drivemeans, and wherein both the drive means and the guide means haverespective central holes therethrough suitable to receive a K-wire.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the proximal ring structure and thedistal ring structure are connected by a guide means and also by a drivemeans comprising a drivescrew, and wherein the drivescrew engagescomplementary threads in the distal ring structure, and the drivescrewcomprises a polymeric material that creates a mechanical interference tobear against the threads.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein the proximal ring structure and thedistal ring structure are connected by a drive means comprising adrivescrew, wherein the drivescrew also comprises a circumferentialgroove that may accept a snap-ring.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a first structure and asecond structure, wherein the first structure and the second structureare connected by a drive means comprising a drivescrew, wherein thedrivescrew comprises a head groove and one of the structures comprises acircumferential internal groove, and further comprising a snap-ring thatpartially occupies the head groove and partially occupies thecircumferential internal groove.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1A is a three-dimensional view of an embodiment of the invention,in a vertically contracted configuration. FIG. 1B is a three-dimensionalview of an embodiment of the invention, in a vertically expandedconfiguration.

FIG. 2 is similar to FIG. 1B but with one endplate omitted for clarityof illustration.

FIG. 3A is a three-dimensional view of the proximal ring structure. FIG.3B is similar to FIG. 3A except from a different vantage point. FIG. 3Cis a three-dimensional view of a section of the proximal ring structuretaken along line 3C-3C of FIG. 3A. FIG. 3D is a top view of the proximalring structure. FIG. 3E is a three-dimensional view of the proximal ringstructure, nearly from the top, with certain dimensions defined.

FIG. 4 is an illustration showing the proximal ring structure in a topview, along with a view that is three-dimensional but nearly a top view,and along with a repeated shape of its central opening, all in order todescribe the central opening of the proximal ring structure.

FIG. 5A is another three-dimensional view of the proximal ringstructure, three-dimensionally but somewhat from the side. FIG. 5B is aview of a section of the proximal ring structure taken along line 5B-5Bof FIG. 5A, nearly from a side. FIG. 5C is a more close-upthree-dimensional view of some of a section of the proximal ringstructure taken along line 5C-5C of FIG. 5A.

FIG. 6A is a three-dimensional view of a portion of the proximal ringstructure, defining certain dimensions. FIG. 6B is a three-dimensionalview of another portion of the proximal ring structure, defining certainother dimensions. FIG. 6C is a three-dimensional view of the proximalring structure, defining certain dimensions.

FIG. 7A is a three-dimensional view of the distal ring structure. FIG.7B is a top view of the distal ring structure. FIG. 7C is athree-dimensional view of the distal ring structure somewhat from anend.

FIG. 8A is a three-dimensional view of a subassembly of the proximalring structure and the distal ring structure. FIG. 8B is a top view ofthe same. FIG. 8C is another three-dimensional view of the same, from adifferent perspective, with the two ring structures positioned relativeto each other in what would be the vertically contracted configurationof the overall device. FIG. 8D is similar to FIG. 8C, but with the tworing structures positioned relative to each other in what would be thevertically expanded configuration of the overall device.

FIG. 9A is a three-dimensional view of an endplate, looking somewhat ata surface of the endplate that would face internally in the assembleddevice. FIG. 9B is a similar three-dimensional view of an endplate, froma different perspective. FIG. 9C is a three-dimensional view of theendplate looking at a surface of the endplate that would face externallyin the assembled device. FIG. 9D is similar to FIG. 9C but viewed morefrom a side. FIG. 9E is a three-dimensional view of the endplate withcertain ramp angles defined. FIG. 9F is another three-dimensional viewof the endplate. FIG. 9G is a view of the endplate showing especiallythe external (bone-facing) surface of the endplate.

FIG. 10A shows, in section, the components of the assembly in the fullyvertically contracted configuration. FIG. 10B shows the same componentsin a partially vertically expanded configuration. FIG. 10C shows thesame components in a fully vertically expanded configuration. FIG. 10Dis similar to FIG. 10C but with a slightly different vantage point andlabeled to show certain dimensions. FIG. 10E is similar but from yetanother vantage point especially to make the urging structure visible.

FIG. 11 is a three-dimensional view of a section of the assembled deviceparticularly illustrating the interaction of the urging structure withother components.

FIG. 12 is a generally top view showing the drivescrew in relation tothe central opening through the endplate and the overall device.

FIG. 13A and FIG. 13B show a load path situation for expansion of thedevice, with FIG. 13A being a section taken at the centerplane, and FIG.13B being a section taken at a plane removed from the centerplane. FIG.13C and FIG. 13D show a load path situation for contraction of thedevice, with FIG. 13C being a section taken at the centerplane, and FIG.13D being a section taken at a plane removed from the centerplane.

FIG. 14A shows in cross-section a portion of the device having thedrivescrew comprising a polymeric friction element and also a snap-ring.FIG. 14B is a three-dimensional view of the drivescrew in isolation,without the polymeric friction element. FIG. 14C is a three-dimensionalview of the drivescrew in isolation, together with its friction element,and with the snap-ring shown exploded away from the drivescrew. FIG. 14Dshows the guide pin.

FIG. 15A is a three-dimensional view of two devices placed in anintervertebral disc space, viewed from an anterior vantage point. FIG.15B is a three-dimensional view of two devices placed in anintervertebral disc space, viewed from a posterior vantage point. FIG.15C is a three-dimensional view of one of the devices being placed in anintervertebral disc space, also showing a portion of an installationinstrument.

DETAILED DESCRIPTION

The present disclosure is directed generally to aspects of a device thatcan be surgically implanted into a patient, and, more specifically, oneor more aspects of a device that can change at least one of itsdimensions after being introduced inside the patient's body. Forexample, some aspects of the present disclosure are directed to entiresystems and methods that can be introduced into the intervertebral discspace for purposes of fusing adjacent vertebrae. Some aspects of thepresent disclosure are directed to one or more aspects of a system andsurgical method.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

In an embodiment of the invention, an expandable support device isdisclosed that can be inserted into a target surgical site with thedevice being in a reduced-height configuration. The device is alsocapable of being reconfigured into an expanded-height configuration. Anembodiment is illustrated in FIG. 1A in its reduced-heightconfiguration, and FIG. 1B in its expanded-height configuration.Reference directional designations, namely longitudinal, vertical andlateral, for discussions purposes, are illustrated in FIG. 1A.

Referring again to FIGS. 1A-1B and also now to FIG. 2, a device 10 of anembodiment of the invention may comprise a central mechanism locatedbetween two endplates and capable of causing the two endplates to movetoward or away from each other. (For clarity of illustration, in FIG. 2one of the endplates is omitted.) The central mechanism may comprise tworing structures, of which one may be designated a proximal ringstructure 100 and the other of which may be designated a distal ringstructure 200. It can be understood that the designations proximal anddistal for the ring structures 100, 200 only refer to a vantage pointfor descriptive purposes and are not essential characteristics. Theproximal ring structure 100 and distal ring structure 200 may be capableof translating relative to each other along an axis that may be referredto as a longitudinal axis. The device 10 may further comprise anactuation mechanism 400 that causes the relative translation between thetwo ring structures 100, 200 along the longitudinal axis. There may alsobe a guide mechanism 500 that engages the two ring structures 100, 200in such a way as to constrain certain degrees of freedom of theirrelative motion.

Proximal Ring Structure

Referring now to FIGS. 3A-3E, proximal ring structure 100 may first ofall comprise a perimeter that extends around a closed path to define anempty interior space that may be referred to as proximal ring structureopening 110. As illustrated, the closed path may comprise, generallyspeaking, in sequence, first side 121, second side 122, third side 123and fourth side 124. As illustrated, at least some of these varioussides may comprise some segments or surfaces that may be substantiallystraight lines or planes. Certain features or surfaces of the first side121 may be parallel to certain features or surfaces of the third side123, although this is not essential. Certain features or surfaces of thesecond side 122 may be parallel to certain features or surfaces of thefourth side 124, although this is not essential. The closed path mayfurther comprise rounded corners on the interior, the exterior or both.

As dimensioned in FIGS. 3A-3E, the proximal ring structure 100 may havean external long end-to-end dimension PEL. This dimension may bemeasured, along the longitudinal direction, between extreme endsurfaces, which may be parallel to each other. As dimensioned in FIGS.3A-3E, the proximal ring structure 100 may have an internal longend-to-end dimension PIL. This dimension may be measured, along thelongitudinal direction, between extreme internal surfaces, which may beparallel to each other.

It is further possible to define, for proximal ring structure 100, a“hybrid” dimension PHL as illustrated in FIG. 3C. This dimension is adistance, along the longitudinal direction, between one internal surfaceand one external surface.

With regard to the sides 122 and 124, it is possible that second side122 and fourth side 124 may each comprise an offset as illustrated, sothat towards one end second side 122 and fourth side 124 are fartheraway from each other and towards the opposite end, second side 122 andfourth side 124 are closer to each other.

As a consequence of the offset, in the lateral direction, the proximalring structure 100 may have two different lateral overall externaldimensions, the first lateral overall external dimension PEW1 in a firstregion, and the second lateral overall external dimension PEW2 in asecond region. Such lateral dimensions may be measured between surfacesthat are parallel to each other. One of the lateral overall externaldimensions may be larger than the other lateral overall externaldimension, for example, PEW1>PEW2. Similarly, the proximal ringstructure 100 may have two different lateral overall internaldimensions, the first lateral overall internal dimension PIW1 in a firstregion, and the second lateral overall internal dimension PIW2 in asecond region. Such lateral dimensions may be measured between surfacesthat are parallel to each other. One of the lateral overall internaldimensions may be larger than the other lateral overall internaldimension, for example, PIW1>PIW2.

Furthermore, it is possible that PIW1>PEW2. The implantable device 10may have a central mechanism comprising a proximal ring structure 100and a distal ring structure 200 (described elsewhere herein), in whichone of the ring structures has four sides, and of those four sides, twoopposed sides (122, 222) have offsets such that there can be defined afirst inside width PIW1 and a second inside width PIW2 and a firstoutside width PEW1 and a second outside width PEW2, wherein the smallerof the outside widths PEW2 is less than the larger of the inside widthsPIW1. This relation may be true for either the proximal ring structure100 or the distal ring structure 200 or both.

Referring now to FIG. 4, a prism is defined here to be athree-dimensional shape that is defined by a two-dimensional base shapethat is repeated or extruded identically in a third directionperpendicular to the base shape. That direction may be referred to asthe prismatic axis direction. The proximal ring structure opening 110may be surrounded by an internal perimeter surface such that at least asubstantial portion of the internal perimeter surface would coincidewith an appropriately shaped prism having a prismatic axis direction. Asillustrated, the proximal ring structure 100 has a proximal ringstructure opening 110 much of whose perimeter would coincide with aprism whose two-dimensional base shape is a shape that may be describedgenerally as a narrower rectangular region merging with a widerrectangular region with all or some corners rounded using segments ofcurves such as circular arcs. The implantable device 10 may have acentral mechanism comprising a proximal ring structure 100 and a distalring structure 200 (described elsewhere herein), in which at least oneof the ring structures 100, 200 has a central opening 110, 210 that hasa first internal width dimension PIW1 and a second internal widthdimension PIW2, wherein the first internal width dimension PIW1 isdifferent from the second internal width dimension PIW2. This relationmay exist for either the proximal ring structure 100 or the distal ringstructure 200. As illustrated in FIG. 4, that described base shape maybe extruded or repeated in the dimension perpendicular to the plane ofthe described shape to produce a prismatic shape, such that asignificant portion of the internal surface of the proximal ringstructure opening 110 (or that portion of the internal surface of theproximal ring structure opening 110 that is itself a prismatic surface)may coincide with the external surface of the prism. (In FIG. 4, some ofthe repetitions of the base shape of the extrusion are omitted forclarity.) Of course, it would be possible to design the proximal ringstructure 100 so that its proximal ring structure opening 110 is definedby a prismatic base shape other than the describedmerged-rounded-rectangular shape. It is understood that, depending ondetails of design of the proximal ring structure 100, it is possible tohave local irregularities in the internal perimeter surface of theproximal ring structure opening 110, so that the internal surface of theproximal ring structure opening 110 might not coincide everywhere withthe described prism. Nevertheless, even if with only a substantialportion of the internal surface of the proximal ring structure opening110 coincides with the described prism, the described prism may serve todefine, by its prismatic axis direction, a direction of the proximalring structure opening 110. More generally, a direction of the proximalring structure opening 110 may be defined as the direction of the axisof a prismatic structure when the prismatic structure is in theorientation that best allows a prism of cross-sectional shape similar tothat of the proximal ring structure opening 110 to fill or pass throughthe proximal ring structure opening 110. This axis may generallycoincide with the vertical direction of device 10.

With continued reference to FIGS. 3A-3E and additionally referring toFIGS. 5A-5C, the proximal ring structure 100 may have a first ramp 131and a second ramp 132. First ramp 131 and second ramp 132 may be locatedin the same direction from the midplane of device 10 at opposite ends ofproximal ring structure opening 110. For example, the proximal ringstructure 100 may have a midpoint in the longitudinal, i.e.,proximal-distal, direction. First ramp 131 may be proximal of themidpoint and second ramp 132 may be distal of the midpoint. For example,first ramp 131 may be part of first side 121, and second ramp 132 may bepart of third side 123. First ramp 131 and second ramp 132 may slope insubstantially the same orientation, i.e., if from a particular viewingdirection first ramp 131 slopes from lower left to upper right, secondramp 132 may also slope from lower left to upper right. The proximalring structure 100 may have a first ramp angle 141 is defined asillustrated in FIG. 5A. The proximal ring structure 100 may have asecond ramp angle 142 defined as illustrated in FIG. 5A. Those two rampangles 141, 142 may be equal to each other, i.e., ramps 131 and 132 maybe parallel to each other.

Proximal ring structure 100 may also comprise additional opposed rampsas shown in FIG. 5B. If first ramp 131 and second ramp 132 areconsidered to be on the top of the proximal ring structure 100, thenramp 181 and ramp 182 may be considered to be on the bottom of proximalring structure 100. Ramp 181 may be identical to or a mirror image offirst ramp 131. Ramp 182 may be identical to or a mirror image of secondramp 132. The midplane may be a plane of symmetry between features onthe top of proximal ring structure 100 and features on the bottom ofproximal ring structure 100.

If ramps 131 and 132 involve a T-shaped projection or a T-shaped grooveas illustrated, there may be additional ramp surfaces associated withthe basic ramps 131, 132. Such surfaces may be parallel to basic rampsurfaces 131, 132. (There may be still other surfaces of proximal ringstructure 100 that are perpendicular to those ramp surfaces.) Forexample, ramp surface 131 a may be parallel to ramp surface 131, and mayface toward ramp surface 131. A possible ramp surface 164 a is discussedelsewhere herein. Associated with ramp surface 132 there may be rampsurface 132 a facing toward ramp surface 132, and there may also be rampsurface 132 b, which may face in the same orientation as ramp surface132.

First ramp 131 may have an engagement feature such that a complementarystructure that it interacts with may engage with first ramp 131 in a waythat guides motion, or prevents disassembly in at least some situations,or both.

Second ramp 132 may have an engagement feature also, which could begeometrically similar to or geometrically different from the engagementfeature present with first ramp 131.

In general an engagement feature could comprise a protrusion and areceiver, one of them on a ramp and the other on a complementary surfaceor component. First of all, it is possible that a protrusion and areceiver could constrain so as to keep the device assembled or preventdisassembly under at least some circumstances or with respect to ascertain direction of possible disassembly motion. Such engagement thatprevents disassembly by motion in a direction generally perpendicular tothe ramp surface may be referred to as interlocking. Alternatively, itis possible that a protrusion and receiver could merely cooperate toform a guide to constrain certain degrees of freedom of motion, withoutpreventing the described disassembly in the described direction ofmotion. This may be referred to as non-interlocking.

One of the ramps 131, 132 may have an engagement feature that is aprotrusion and the other of the ramps 131, 132 may have an engagementfeature that is a receiver. As illustrated, second ramp 132 has aprotrusion feature and first ramp 131 has a receiving feature. However,other designs are also possible. Various surfaces of these engaginggeometries may be parallel to each other or perpendicular to each other;as illustrated the various protruding or receiving features havecross-sectional shapes that are rectangles or portions of rectangles.The implantable device 10 may have a central mechanism comprising aproximal ring structure 100 and a distal ring structure 200 (describedelsewhere herein), in which the proximal ring structure 100 has a firstramp 131 and a second ramp 132, in which the first ramp 131 comprises areceiving structure capable of engaging a first complementary shape, andthe second ramp 132 comprises a protruding shape capable of engaging asecond complementary shape.

As illustrated, the two ramps 131, 132 have engagement geometries thatare in the same shape family as each other, i.e., both involve aT-shaped projection engaging a T-shaped receiver that is complementaryto it. However, it is also possible that the two ramps 131, 132 couldhave engagement features that are not the same shape family as eachother (e.g., one could involve T-shape and the other could involvedovetail), or one ramp could involve a feature that preventsdisengagement by motion generally perpendicular to the ramp surface andanother ramp might only involve a feature that guides motion withoutpreventing disassembly as does not prevent disassembly as described, andmight not involve any such interlocking feature.

It can be noted that it is possible to have protrusion and receivingfeatures that prevent disengagement between engaging components thatinvolves motion in the direction of simply pulling the ramps apart fromeach other in a direction generally perpendicular to the ramp surfaces.The described T-shaped projection and T-shaped groove accomplish suchprevention of disengagement. The prevention of disengagement couldalternatively be accomplished by a dovetail engagement such as atrapezoidal shape engaging with a complementary shape, or by still othergeometry. Alternatively it is possible to have protrusion and receivingfeatures that restrict or guide some degrees of freedom of motion whilenot actually preventing the described disengagement in the describeddirection of motion. An example of such a geometry would be a projectionwhose cross-section is a simple rectangle, and a receiving feature thatis complementary to it. Of course, still further, it would also bepossible to have a mixture of such kinds of features in various rampswithin the same device or component.

As illustrated, the engagement features of the first ramp 131 and thesecond ramp 132 in proximal ring structure 100 are of the same type aseach other, i.e., both are in the form of either a T-shaped groove or aT-shaped projection. As illustrated, the one engagement feature is aT-shaped projection and another engagement feature is a T-shapedreceiver, each of which is suitable to mate with a complementary shape.However, the various ramp engagement features could also be differentfrom each other.

In FIGS. 6A-6C are shown various specific dimensions of the engagementfeatures of proximal ring structure 100. Some of the features pertain tothe protrusion and some pertain to the receiver. Interrelationships ofthese dimensions with dimensions of other parts are described elsewhereherein.

It can further be noted that in connection with first ramp 131 andsecond ramp 132, there may be associated still other surfaces that maybe parallel to first ramp 131 and second ramp 132. These other surfacesmay be associated with engagement features. In describing ramps, thedescription outward-facing is used herein to describe a ramp surfacesuch as 131, 132 that faces the overall corresponding component againstwhich the ramp faces, and which could potentially bear force against itsface during vertical expansion of the overall device 10. The oppositedescription, of an inward-facing ramp, is for a ramp surface such as 131a, 132 a that serves as a capture feature preventing disassembly of thedevice by disassembly motion of ramp surfaces away from each otherperpendicular to the ramp surface, or which bears or could potentiallybear force during vertical contraction of the overall device 10. It canfurther be noted that sometimes there may be a second paralleloutward-facing surface such as 132 b related to a particular rampstructure. Depending on dimensions and tolerances in proximal ringstructure 100 and also in an engaging part, either or both of suchsurfaces 131, and 132, 132 b could be active in sliding and generationof forces involving that ramp for causing vertical expansion of thedevice 10.

The proximal ring structure 100 may, on its second side 122 and fourthside 124 (the portions of those sides that are larger in the lateraldirection) have side ramps 162, 164 that may be a portion of a generallytrapezoidal shape. These side ramps 162, 164, although rounded surfacesmay be present, may have some straight-line or planar segments that havea defined slope. Side ramp 162 may be part of second side 122, and sideramp 164 may be part of fourth side 134. The side ramps or cutouts 162,164 may have a slope corresponding to the angled sides of the generallytrapezoidal shape. This slope of side ramps or cutouts 162, 164 may beidentical to the slope of ramp 131, or ramp 132, or both. This isdiscussed further elsewhere herein. These side ramps 162, 164 areillustrated as being simple ramps that do not comprise engagementfeatures for engagement with a complementary feature of anothercomponent. Geometric transitions to or from side ramps 162, 164 maycomprise rounded corners. It is also possible that a ramp such as 164may have a flat surface that continues in an irregular shape asdesignated 164 a in FIG. 5C.

It is possible to define a centerplane that extends in a verticaldirection and includes the longitudinal axis of the device 10. It canfurther be noted that the first ramp 131 and the second ramp 132 areramps that straddle both sides, in a lateral direction, of acenterplane. In contrast, side ramp 162, exists entirely on one side (ina lateral direction) of the centerplane, and side ramp 164 existsentirely on the other side (in the lateral direction) of thecenterplane. It can further be noted that side ramps 162, 164 may becoplanar with each other and that ramp 131 may be parallel to but notcoplanar with side ramps 162, 164. Side ramps 162, 164 may also bereferred to as overhang-receiving cutouts, due to their receipt of andinteraction with overhangs of an endplate described elsewhere herein.The device 10 may have a central mechanism comprising a proximal ringstructure 100 and a distal ring structure 200 (described elsewhereherein), such that the proximal ring structure 100 has a first ramp suchas 131 or 132 that extends continuously across the centerplane, and suchthat the proximal ring structure 100 also has two additional ramps suchas 162, 164, one on each side of the centerplane, and not intersectingthe centerplane, with the two additional ramps 162, 164 being coplanarwith each other.

It can be noted that the proximal ring structure 100, as described andillustrated, comprises both at least one ramp that has an engagementfeature, such as ramps 131, 132 (possibly 131 a, 132 a depending ondimensions and tolerances), and at least one ramp that does not have anengagement feature, such as 162, 164. An engagement feature can refer toeither a protrusion or a receiving feature, any of which may be eithernon-interlocking or interlocking. It is possible that a ramp having anengagement feature and a ramp not having an engagement feature may occuron a particular direction relative to the proximal-distal midpoint ofproximal ring structure 100, with respect to the longitudinal directionof the device 10. The implantable device 10 may have a central mechanismcomprising a proximal ring structure 100 and a distal ring structure 200(described elsewhere herein), in which the proximal ring structure 100has a plurality of ramps such as 131, 132, 162, 164, in which at leastone of the ramps has an engagement feature and another of the ramps doesnot have an engagement feature. An engagement feature may be either aprotrusion or a receiving feature, and may be either interlocking ornon-interlocking. It can further be noted that the proximal ringstructure 100, as described and illustrated, contains three differentoutward-facing ramp surfaces, such as 131, 132 and either 162 or 164that are parallel to each other but are located in different respectivenon-coplanar planes. More generally, 131, 132, 132 b and the grouping of162, 164 may all be outward-facing ramp surfaces that are parallel toeach other but are located in different respective non-coplanar planes.Ramp surfaces 131 a, 132 a may also be parallel to those others as wellalthough not themselves being outward-facing.

It can further be noted that on any given direction from theproximal-distal midpoint of the proximal ring structure 100, there canbe a mixture of different kinds of ramps: one or more ramps that have notype of engagement feature, along with one or more ramps that have sometype of engagement feature. The ramps used in this description can bespecified as outward-facing as in the illustrations or could be any typeof ramp either outward-facing or not.

It can further be noted that a T-shaped projection in combination with acomplementary-shaped receiver such as a T-shaped slot, as illustrated,constrains against disassembly in a direction perpendicular to the rampsurface, and may be referred to as interlocking. A dovetail (trapezoidalcross-section) in combination with a complementary-shaped receiver wouldalso constrain against disassembly. Other shapes of engagement featuresare possible. For example, a protrusion of simple rectangularcross-section, in combination with a complementary-shaped receivingstructure, would constrain certain degrees of freedom of motion butwould not actually constrain against disassembly in a directionperpendicular to the ramp surface, and may be referred to asnon-interlocking.

It is possible to define the proximal-distal midpoint that is midwaybetween the extremes of the proximal ring structure 100 in aproximal-distal (longitudinal) direction. It can be noted that withinthe proximal ring structure 100, there can be as many as four differentoutward-facing ramp surfaces that are parallel with each other but alllie in different planes. These can be 132, 132 b, 131 and the groupingof 162, 164. Further counting ramp surfaces that are not outward-facing,there may additionally be ramp surfaces 131 a, 132 a, which also may beparallel to the just-mentioned ramp surfaces and need not be coplanarwith any of them. In one direction from proximal-distal midpoint ofproximal ring structure 100, counting ramp surfaces that may be eitheroutward-facing or non-outward-facing, there may be the followingparallel non-coplanar ramp surfaces: 131, 131 a and the grouping 162,164. In the other direction from the proximal-distal midpoint, there maystill further be ramp surfaces 132, 132 a, 132 b, being parallel to andnon-coplanar with each other.

A ramp surface can have a slope direction, which may be defined suchthat the slope direction is contained in the ramp surface plane, andsuch that the slope direction and the longitudinal direction of theimplantable device 10 can form an angle. With respect to the slopedirection, a width can be defined as being measured within the rampplane in a direction perpendicular to the slope direction, and measuringthe extent within which the ramp surface is truly planar, i.e., to apoint at which the surface departs from planarity such as by a corner ora fillet etc. In the example as shown, it can be observed that the widthof surface of ramp 131 or 132 or 132 a is different from the width ofsurface of ramp 162 on second side 122 or ramp 164 on the fourth side124. Similarly, other comparisons of ramp surfaces on the proximal ringstructure 100 would also show unequal ramp widths. It is furtherpossible, alternatively, that either or both of the surface of secondside 122 in the region illustrated by ramp 162, and the surface offourth side 124 in the region illustrated by ramp 164, may, instead of aplanar ramp surface, have a rounded surface (not shown) extending fromthe interior to the exterior of that respective side. Such a roundedsurface may have a tangent line that is straight generally lying in avertical plane and may be suitable for a corresponding ramp surface,such as a ramp surface of an endplate, to slide along it. Such a roundedsurface may function similarly to a ramp surface (such as 162, 164) ininteracting with a corresponding ramp surface of another component ofdevice 10.

The proximal ring structure 100 may have, at one end such as first end121, an interface with the actuation mechanism 400. The interface withthe actuation mechanism 400 may comprise a cylindrical hole 180 in firstend 121 of proximal ring structure 100, or other similar details asknown in the art. The cylindrical hole may comprise a counterbore withan internal groove 196 as described elsewhere herein, or other features.The proximal ring structure 100 may have a feature (not shown) suitableto interact with a surgical instrument such as to be grasped by asurgical instrument. The surgical instrument interface feature may be atthe same end of the proximal ring structure 100 as the actuationmechanism 400.

At an opposed end, such as at third side 123, proximal ring structure100 may have an interface with a guide mechanism 500. The interface withthe guide mechanism 500 may comprise a hole 190 as illustrated, oralternatively a cylindrical post, or means to join with any suchfeature, or other details known in the art. Hole 190 may be internallythreaded, or may be a simple cylindrical hole, or other design as knownin the art.

Distal Ring Structure

Referring now to FIGS. 7A-7C, there may also be provided a distal ringstructure 200. Some features of distal ring structure 200, such as itsgeneral shape, may have similarity to corresponding features of proximalring structure 100, but other features may be different. Distal ringstructure 200 may comprise a perimeter that extends around a closed pathto define an empty interior space that may be referred to as distal ringstructure opening 210. As illustrated, the closed path may comprise,generally speaking, in sequence, first side 221, second side 222, thirdside 223 and fourth side 224. As illustrated, at least some of thesevarious sides may comprise some segments or surfaces that may besubstantially straight lines. Certain features or surfaces of the firstside 221 may be parallel to certain features or surfaces of the thirdside 223, although this is not essential. Certain features or surfacesof the second side 222 may be parallel to certain features or surfacesof the fourth side 224, although this is not essential. The closed pathmay further comprise rounded corners either internally or externally.

The distal ring structure 200 may have a blunt nose 215 suitable todisplace bodily tissue without injuring it as the device 10 is advancedinto bodily tissue during surgery.

As dimensioned in FIG. 7B, the distal ring structure 200 may have anexternal long end-to-end dimension DEL. This dimension may be measured,along the longitudinal direction, between extreme end surfaces, whichmay be parallel to each other. Also as dimensioned in FIG. 7, the distalring structure 200 may have an internal long end-to-end dimension DIL.This dimension may be measured, along the longitudinal direction,between extreme internal surfaces, which may be parallel to each other.

It is further possible to define, for distal ring structure 200, a“hybrid” dimension DHL as illustrated in FIG. 7B. This dimension is adistance, along the longitudinal direction, between one internal surfaceand one external surface.

It is further possible that second side 222 and fourth side 224 may eachcomprise an offset as illustrated, so that towards one end second side222 and fourth side 224 are farther away from each other and towards theopposite end, second side 222 and fourth side 224 are closer to eachother.

As a consequence of the offset, in the lateral direction, the distalring structure 200 may have two different lateral overall externaldimensions, the first lateral overall external dimension DEW1 in a firstregion, and the second lateral overall external dimension DEW2 in asecond region. Such lateral dimensions may also be measured betweensurfaces that are parallel to each other. One of the lateral overallexternal dimensions may be larger than the other lateral overallexternal dimension, for example, DEW1>DEW2. Similarly, the distal ringstructure 200 may have two different lateral overall internaldimensions, the first lateral overall internal dimension DIW1 in a firstregion, and the second lateral overall internal dimension DIW2 in asecond region. Such lateral dimensions may also be measured betweensurfaces that are parallel to each other. One of the lateral overallinternal dimensions may be larger than the other lateral overallinternal dimension, for example, DIW1>DIW2. Furthermore, it is possiblethat DIW1>DEW2.

The distal ring structure 200 may have, at one end, an interface withthe actuation mechanism 400, and may have, at an opposed end, aninterface with the guide mechanism 500. The interface with the actuationmechanism 400 may comprise a threaded hole 270 in first side 221,suitable to receive a threaded member.

The distal ring structure opening 210 may have a distal ring structureopening direction, which may be defined in a manner similar to thatdiscussed for the proximal ring structure opening 110.

It is further possible that the distal ring structure 200 may comprise aprojection in the vertical direction, which may be referred to as anurging structure 250. As illustrated, the urging structure 250 projectsboth upwardly and downwardly in the vertical direction from first side221. This urging structure 250 may interface with other components ofthe device 10 as described elsewhere herein. The urging structure 250may have a dimension in the longitudinal direction DULON as defined inFIG. 7A, which dimension may be involved in interfacing with othercomponents as discussed elsewhere herein. Also, the mostvertically-extending portion of urging structure 250 may have a lateraldimension DULAT that is less than the smaller internal width DIW2 ofdistal ring structure 200 adjacent to urging structure 250. Also, wherethe urging structure 250 merges with the rest of end at first side 221,there may be a transition shape 252 that also may be involved ininterfacing with other components as discussed elsewhere herein.

The distal ring structure 200, on its second side 222 and fourth side224 (the portions of those sides that are larger in the lateraldirection) may have overhang-receiving cutouts or ramps 262, 264 thatmay be a portion of a generally trapezoidal shape. The cutouts or ramps262, 264 may have a slope corresponding to the angled sides of thetrapezoidal shape. This slope may be equal to the slope of any or all oframps 131, 131 a, 132, 132 a, 132 b of proximal ring structure 100.Shape transitions associated with the trapezoidal shape may compriserounded corners. This is discussed further elsewhere herein.

In the longitudinal direction, the urging structure 250 may be such asto fit between the stability bar 370 and the depending structure fromthe endplate 300 that forms the edge of endplate central opening 310.For example, in the longitudinal direction, the urging structure 250 mayhave two opposed sides that are generally parallel to each other anddefine an external dimension between them. Similarly, the stability bar370 and the depending structure from the endplate 300 that forms theedge of endplate central opening 310 may have surfaces that face eachother and are generally parallel to each other and define an internaldimension between them in the longitudinal direction. The dimension ofurging structure 250, in the longitudinal direction, may be justslightly less than or may be approximately equal to, the distancebetween the internal surface of endplate central opening 310 and thefacing edge of stability bar 370.

Interrelationships Between the Two Ring Structures

Generally speaking, the proximal ring structure 100 and the distal ringstructure 200 may have with each other an intertwining relationship sothat in either the lateral or the longitudinal direction, in some placesone ring structure is more exterior and in other places the other ringstructure is more exterior. When considering the proximal ring structure100 and the distal ring structure 200 in conjunction with each other, itis possible to note some dimensional interrelationships that may existbetween the two ring structures.

When the proximal ring structure 100 and the distal ring structure 200are assembled together in a sub-assembly, the proximal ring structureopening 110 may partially but not completely overlap with the distalring structure opening 210 when viewed along the first openingdirection. The assembly containing proximal ring structure 100 anddistal ring structure 200 can have an open region 12 passing through thecenter of the device 10 along the direction of the proximal ringstructure opening 110 and the distal ring structure opening 210. Thedimensions of this open region 12 may vary with the relative positionsof proximal ring structure 100 and distal ring structure 200 withintheir range of permitted motion, but the open region 12 may exist to atleast some extent throughout the permitted range of relative motion ofproximal ring structure 100 and the distal ring structure 200. Thesub-assembly may allow relative translational motion between the tworing structures 100, 200 and may leave some open central region 12 forall permitted translational positions of the two ring structures 100,200.

It is possible that the larger external width dimension PEW1 of theproximal ring structure 100 may be at least approximately equal to thelarger external width dimension DEW1 of the distal ring structure 200.This may provide a somewhat consistent external size envelope of theoverall device 10. It is possible that the smaller internal widthdimension PIW2 of the proximal ring structure 100 may be at leastapproximately equal to the smaller internal width dimension DIW2 of thedistal ring structure 200. This may help to provide a somewhatconsistent size of open region 12 that generally passes in the verticaldirection through the sub-assembly of proximal ring structure 100 anddistal ring structure 200. It is further possible that PEW2 may be atleast approximately equal to DEW2 and that PIW1 may be at leastapproximately equal to DIW1.

In order to permit the intertwining or nesting of the two ringstructures 100, 200, the appropriate internal width of one ringstructure may be at least a slight amount greater than the correspondingexternal width of the other ring structure. For example, the largerinternal width, PIW1, of proximal ring structure 100, may be larger thanthe smaller external width DEW2 of distal ring structure 200. Similarly,the larger internal width, DIW1, of distal ring structure 200 may belarger than the smaller external width PEW2 of proximal ring structure100. The existence of a slight clearance gap between those respectivedimensions may be chosen so as to allow relative motion, especiallytranslation, to occur freely between those two ring structurecomponents. However, the clearance gap may be small enough so that itlimits any permitted angular tilting of one ring structure with respectto the other ring structure, around an axis coincident with thelongitudinal direction, to a suitably small magnitude.

In an embodiment of the invention, the proximal ring structure 100 andthe distal ring structure 200 may be arranged such that, in allpermitted positions of the distal ring structure 200 relative to theproximal ring structure 100, in a section of the device 10 taken along alongitudinal direction, there is a first end at first side 121 of theproximal ring structure 100, followed by a first end at first side 221of the distal ring structure 200, followed by a second end at third side123 of the proximal ring structure 100, followed by a second end atthird side 223 of the distal ring structure 200.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structureand a distal ring structure, wherein, in some cross-section taken in afirst plane perpendicular to a longitudinal direction, there is insequence progressing in a lateral direction the proximal ring structure100 followed by the distal ring structure 200 followed by some emptyspace followed by the distal ring structure followed by the proximalring structure, and wherein, in some other cross-section taken in asecond plane perpendicular to the longitudinal direction, there is insequence progressing in a lateral direction the distal ring structurefollowed by the proximal ring structure followed by some empty spacefollowed by the proximal ring structure followed by the distal ringstructure.

In an embodiment of the invention, there may be provided an implantabledevice having a central mechanism comprising a proximal ring structure100 and a distal ring structure 200 and having a central opening,wherein, in sequence progressing around the perimeter of the centralopening, the central opening is bounded on the first end by the proximalring structure 100, and then on the first side is bounded first by theproximal ring structure 100 and then by the distal ring structure 200,and then on the second end is bounded by the distal ring structure 200,and then on the second side is bounded first by the distal ringstructure 200 and then by the proximal ring structure 100.

With respect to still other directions, it is possible that proximalring structure 100 and the distal ring structure 200 may have roughlyequal heights along the direction of the proximal ring structure opening110 and the distal ring structure opening 210 i.e., generally thevertical direction of the device 10. It is also possible that proximalring structure 100 and the distal ring structure 200 may have roughlyequal external lengths, i.e., PEL and DEL may be roughly equal. It isalso possible that proximal ring structure 100 and the distal ringstructure 200 may have roughly equal internal lengths, i.e., PIL and DILmay be roughly equal. It is also possible that proximal ring structure100 and the distal ring structure 200 may have roughly equal hybriddimensions, i.e., PHL and DHL may be roughly equal.

Also, the transition along second and fourth sides 122, 124 and 222, 224of proximal ring structure 100 and distal ring structure 200respectively, may involve diagonal segments. These diagonal segments maybe arranged so that at the expanded-height configuration the diagonalsegments either contact each other or have at least a small amount ofspace between them, and at the reduced-height configuration the diagonalsegments have a greater amount of space between them.

When assembled together in an assembly, the proximal ring structure 100and the distal ring structure 200 may be movable with respect to eachother. Such motion may include translation along the longitudinaldirection. Such motion may be driven by an actuation mechanism 400 andmay further be guided by a guide mechanism 500, both described elsewhereherein. FIGS. 8A-8D shows the proximal ring structure 100 and the distalring structure 200, with all other components omitted for clarity ofillustration, at two different relative positions for differenthorizontal translation.

Of the proximal ring structure 100 and the distal ring structure 200,there may be considered to be a driving ring structure and a driven-ringstructure. The proximal ring structure 100 may be considered to bedriving the ring structure in the sense that it may be most proximal tothe surgeon and may be interfaced by an insertion tool. The distal ringstructure 200 may be considered to be the driven ring structure, whichis movable with respect to the driving ring structure. Such movablerelation may include at least translation. Actuation mechanism 400 maycomprise a drivescrew. As described herein, the driven ring structuremay be the ring structure that has an internal thread that receives andthreadingly engages the threads of the drivescrew 450. The driving ringstructure may be considered to be the ring structure that has unthreadedinteraction with the drivescrew. However, it would also be possible tohave configurations in which the opposite is true as far as which ringstructure has threaded interaction with the drivescrew and which ringstructure has unthreaded interaction with the drivescrew.

As a result of some of the dimensional interrelationships such as thoseinvolving internal width dimensions, it is possible that when theproximal ring structure 100 and the distal ring structure 200 areassembled to each other, the appearance of the central opening or region12 that is clear of both the proximal ring structure 100 and the distalring structure 200 may have the general appearance of a rectangle,possibly with rounded corners. This is illustrated with a view along thevertical direction in FIG. 8B.

It can be described that the central opening or region 12 between theproximal ring structure 100 and the distal ring structure 200 may bebounded, in sequence progressing in a lateral direction, on a first sideby the proximal ring structure 100, then on a second side by theproximal ring structure 100 followed by the distal ring structure 200,then on a third side by the distal ring structure 100. Morespecifically, when viewed along the longitudinal axis, the centralopening between proximal ring structure 100 and distal ring structure200 may be bounded by a perimeter of the central opening such that thecentral opening is bounded on an end by the first side 121 of proximalring structure 100, is bounded on its first side by the second side 122of proximal ring structure 100 and thence by the second side 222 ofdistal ring structure 200, then is bounded at an end by the third side223 of distal ring structure 200, then is bounded on another side by thefourth side 224 of distal ring structure 200 and then by the fourth side124 of proximal ring structure 100.

Endplates

Referring now to FIGS. 9A-9G, an embodiment of the invention may furthercomprise a top endplate 300, as described here. There may also be abottom endplate 300. As illustrated, the top endplate 300 and bottomendplate 300 are geometrically identical to each other and are placed onopposite sides of a central plane of symmetry of the device. It is alsopossible that the top and bottom endplates 300 could be mirror images ofeach other with respect to some plane of symmetry such as the midplaneof the device 10. Of course, it is also possible that geometricdifferences could exist between the two endplates.

The endplate 300 may have an external surface 302 suitable to be incontact with a vertebra or other bony surface of a patient's body, andmay have an underside surface opposed to the external surface 302. Theendplate may have an axis, which may at least approximately coincidewith the vertical axis of the overall device 10, and which may be aprismatic direction of a central opening 310 through endplate 300. Onthe external surface 302, the endplate 300 may have one or morelocalized features such as teeth, rails, ridges, grooves, knurling orcombinations thereof, for example on the external or bone-facing surface302. Despite the possible presence of such localized features, theexternal surface 302 may be described by an enveloping external surface304 that may coincide with repeated aspects of repeated features of theexternal surface 302. As illustrated, the enveloping external surface304 may be a plane or slightly curved surface that is approximatelyperpendicular to the vertical axis of the endplate 300. However, ifdesired, the endplate 300 can include a lordosis or other angle definedbetween the enveloping external surface 304 and a plane that isperpendicular to the vertical axis.

As illustrated, the ridges or grooves can have a pitch (distance betweencorresponding repeated features) and can have a leading angle and atrailing angle. One of the angles, i.e., leading or trailing angles, canbe from about 30° to about 90°, for example about 50°. The leading angleand the trailing angle can be unequal to each other so as to provide apreferred direction of sliding of the overall device 10 with respect toadjacent tissue such as vertebral surfaces.

The endplate 300 may have a central opening 310 therethrough. The shapeand dimensions of the central opening 310 may be defined as the shapeand dimensions, in a cross-section perpendicular to the prismatic axisof the prismatic solid, of the largest-cross-section prismatic solidthat will fit through the central opening 310. This shape may be atleast approximately a rectangle with rounded corners. The perimeter ofthe central opening 310 may meet the external surface 302 of theendplate 300 at an edge.

The endplate 300 may comprise a projection which may be referred to as astability bar 370, which may depend away from the external surface 302of the endplate 300. In the longitudinal direction, the stability bar370 may occupy less than the full length of endplate 300. In across-section taken perpendicular to the vertical axis of the endplate300, the stability bar 370 may have a cross-section that is generallyrectangular, but which may include rounded corners. There may be a pairof stability bars 370, opposed to each other, one on each side of acenterplane of the endplate 300. The stability bars 370 may be symmetricor mirror-image with respect to each other. The stability bars 370 mayhave parallel surfaces facing each other internally, defining a distancetherebetween in the lateral direction. The distance between the twostability bars 370 that face each other may be the same as the lateraldimension of the central opening 310 through the endplate 300 at thelocation of the stability bars 370.

The top endplate 300 can comprise, on a surface opposed to the externalsurface 302, a first endplate ramp 331 near one end of the endplate 300and a second endplate ramp 332 near the opposite end of the endplate300. The two ramps 331, 332 can face in the same direction as eachother, and may be described as outward-facing as discussed elsewhereherein. The two ramps 331, 332 may have ramp angles as defined in FIG.9E. The two ramps 331, 332 may be parallel to each other. There mayfurther be additional ramp surfaces 331 a, 331 b, 332 a, 332 b, whichmay be parallel to each other or to ramps 331, 332. The bottom endplate300 can have similar features as the top endplate 300.

Any or all of the ramps can extend at a ramp angle with respect to thelongitudinal axis of device 10. The absolute value of the ramp angle canbe from about 10° to about 75°, more narrowly from about 25° to about60°, yet more narrowly from about 40° to about 50°.

The ramps may comprise features suitable to engage with othercomplementary features on other components. As illustrated, one of theramps 331, 332 has an engagement feature that comprises a protrusion.The other of the ramps 331, 332 has an engagement feature that comprisesa receiving shape. As illustrated, ramp 331 has the protrusion and ramp332 has the receiver. As illustrated, one of the ramps has a T-shapedgroove and the other ramp has a T-shaped projection. However, otherdesigns are also possible. Various surfaces of geometries such asT-shaped geometries may be parallel to each other or perpendicular toeach other. In connection with a T-shaped projection or a T-shapedreceiver, there can be inward-facing surfaces also. Various suchdimensions are defined in FIGS. 9A-9G. Dimensional interrelationshipswith dimensions of other components of device 10 are described elsewhereherein or may be as would be expected in order to permit the variousparts to fit together.

In an embodiment of the invention, there may be provided an implantabledevice 10 having a central mechanism and an endplate 300, wherein theendplate 300 comprises a first outward-facing ramp (such as 331, 332)straddling both sides of a centerplane of the endplate 300, and furthercomprises further comprises a distinct separate outward-facing side ramp(such as ramps on 362, 364, 366 and 368) located so as not to intersectthe centerplane of the endplate 300.

The various ramps, overhangs and other features as described may incombination provide, on the endplate 300, a first ramp surface (such as331 or 332) and a second outward-facing ramp surface (such as 331 or332), wherein the first ramp surface comprises a protrusion and thesecond ramp surface comprises a receiver.

The various ramps, overhangs and other features may be such that theimplantable device 10 has a central mechanism and an endplate, whereinthe endplate comprises a first outward-facing ramp surface that has anengagement feature (such as ramp 331 or 332) and a second outward-facingramp surface that does not have an engagement feature (such as rampsurfaces 362, 364, 366, 368).

The various ramps overhangs and other features as described may incombination provide, on the endplate 300, a first outward-facing rampsurface (such as 331 or 332) and a second outward-facing ramp surface(such as 331 or 332) and a third outward-facing ramp surface (such asramp surfaces 362, 364, 366, 368), wherein the first, second and thirdoutward-facing ramp surfaces lie in different planes and are parallel toeach other.

There can be four different outward-facing ramp surfaces, such as 362,364, 366, 368, and also 331, 331 b, 332, 332 b. There can be threeoutward-facing non-coplanar ramp surfaces, which may be parallel to eachother. There may be three non-coplanar ramp surfaces in any one side, inthe longitudinal direction, from the proximal-distal midpoint.

The endplates 300 may comprise overhanging guides 372, 374, 376, 378. Asillustrated, there are two overhanging guides 372, 374 on one side ofendplate 300, and two more overhanging guides 376, 378 on the other sideof endplate 300. When viewed from a lateral direction, the overhangingguides 372, 374, 376, 378 may have a generally trapezoidal shape,possibly with rounded corners. The sloped sides of the overhangingguides 372, 374, 376, 378 may have an angle that generally matches theangles of the ramps 362, 364 and of ramps 162, 164, 262, 264.

A ramp surface can have a slope direction, which may be defined suchthat the slope direction is contained in the ramp surface plane, andsuch that the slope direction and the longitudinal direction of theimplantable device 10 can form an angle. With respect to the slopedirection, a width can be defined as being measured in a directionperpendicular to the slope direction, and measuring the extent withinwhich the ramp surface is truly planar, i.e., to a point at which thesurface departs from planarity such as by a corner or a fillet etc. Inthe example as shown, it can be observed that there are variousdifferent widths for ramp surfaces 331, 331 a, 331 b, 332, 332 a, 332 b,and the width(s) of surface of ramps on features 362, 364, 366, 368.Similarly, other comparisons of ramp surfaces on the endplate 300 wouldalso show unequal ramp widths. The various ramps, overhangs and otherfeatures as described may in combination provide, on the endplate 300, afirst ramp surface (such as 331 or 332) and a second outward-facing rampsurface (such as 331 or 332), wherein the endplate comprises a firstoutward-facing ramp surface and a second outward-facing ramp surface,wherein the first and second ramp surfaces are of unequal widths.

The slope angle of any or all of ramps 131, 131 a, 132, 132 a, 132 b,162, 164 may generally equal the slope of ramps 331, 331 a, 331 b, 332,332 a, 332 b, 362, 364, 366, 368.

With continued reference to FIGS. 9A-9G particularly FIG. 9G, it ispossible that one of the ramps 331, 332 or its associated engagementfeatures, or both, can intersect the external surface 302 of endplate300 at an edge that is a part of the perimeter or edge where centralhole 310 passes through the endplate 300, such through as the externalsurface 302 of endplate 300.

It is further possible that endplate 300 can have a recess such assemicylindrical recess 388, 389 that may accommodate a portion of thedrive mechanism 400 or the guide mechanism 500.

The device may further comprise a gentle curve on the endplates and mayhave fillets or rounded corners in various places such as places thatabut bodily tissue.

Dimensional and Design Interrelationships Involving the Endplates

Referring now to FIGS. 10A-10E, there may exist certain geometricrelationships among the proximal ring structure 100, the distal ringstructure 200, the urging structure 250 connected to or integral withdistal ring structure 200, and the endplates 300 including the stabilitybars 370 that are connected to the endplates 300.

The ramp angle 341, 342 of the ramps 331, 332 of endplate 300 may equalthe ramp angle 141, 142 of the ramps 131, 132 on the proximal ringstructure 100. The device 10 can have an internal paired expansionsliding interface. The expansion sliding interface can include the rampwedges slidably interfacing with complementary ramp surfaces of theendplates 300. The interface between the ramp wedges and the endplatewedges can include direct contact, such as a flat abutment, guides,rails, grooves, tracks, T-slots or combinations thereof. The variousramps and features such as protrusions or receivers may have localdimensions that enable them to fit with and interengage the ramps in theproximal ring structure 100 or other complementary shapes.

The vertical dimension of the urging structure 250 may be such that evenat the maximum vertical expansion of the device 10, the urging structure250 maintains contact with corresponding aspects of the endplate 300,i.e., the urging structure 250 may maintain contact with the interior ofendplate central opening 310. The urging structure 250 may also maintaincontact with stability bar 370. In particular, the shape and dimensionsof urging structure transition region 252 may be such as to maintainsuch contact throughout a desired range of motion of the variouscomponents of device 10.

Referring now to FIGS. 10A-10E, there is illustrated a possiblerelationship, in the lateral direction, between the stability bars 370and the proximal ring structure 100 and the distal ring structure 200.The laterally-outward-facing surface of the stability bars 370 may beclosely-fitting with the inward-facing surface of the proximal ringstructure 100 and the distal ring structure 200. Stated differently, theexternal lateral dimension between laterally opposed pairs of stabilitybars 370 can be such as to just fit inside the proximal ring structure100 and the distal ring structure 200. This is illustrated in FIGS.10A-10C, which shows a cross-sectional view for three different heightsof the overall device (minimum, intermediate and maximum heights).

The stability bar 370 of the top endplate 300 can abut the stability bar370 of the bottom endplate 300 when the device 10 is in a fullyvertically contracted configuration. The lateral dimension of the urgingstructure 250, at its point most vertically distant from the midplane ofthe device 10 (the midplane being a plane perpendicular to the verticaldirection), may be smaller than or approximately equal to the lateraldimension of the central opening 310 through endplate 300.

In the lateral direction, the urging structure 250 (particularly theportion of urging structure 250 farthest from the midplane of device 10)may have an external lateral dimension, which may be defined betweenparallel surfaces. This external lateral dimension of thevertically-outward-most part of urging structure 250 may be smaller thanor approximately equal to the lateral dimension of the central opening310 through endplate 300. The distal ring structure 200 may have asmallest internal width in a lateral direction. The external lateraldimension of the vertically-outward-most part of urging structure 250may be smaller than the smallest internal width of the distal ringstructure 200 in a lateral direction. The proximal ring structure 100may have a smallest internal width in a lateral direction. The externallateral dimension of the vertically-outward-most part of urgingstructure 250 may be smaller than the smallest internal width of theproximal ring structure 100 in a lateral direction.

Upon actuation of the actuation mechanism 400 so as to cause verticalexpansion of the overall device 10, the urging structure 250 may urgeagainst an internal surface of opening 310 of the endplate 300 to causeendplate 300 to ride upward along the ramp structure 131, 132 andthereby cause expansion of the overall device 10 in the verticaldirection. Upon actuation of the actuation mechanism 400 so as to causecontraction of the overall device 10, the urging structure 250 may urgeagainst the stability bar 370 to cause endplate 300 to ride downwardalong the ramp structure 131, 132 (with the endplate 300 possibly alsohaving interacting with the related ramp surfaces 131 a, 132 a) andthereby cause contraction of the overall device 10 in the verticaldirection. In order to accomplish this, there may be an interrelationamong the various parts such that the transition region 252 of urgingstructure 250 of distal ring structure 200 makes appropriate contactwith stability bar 370. Such contact may serve to urge stability bar 370and hence endplate 300 as a whole to move in a direction that wouldcontract the vertical height of device 10. In general, urging structure250 may, in a longitudinal direction, fit between stability bar 370 andan internal surface of central opening 310 of endplate 300.

As discussed, proximal ring structure 100 and distal ring structure 200may have ramps 162, 164, 262, 264, which may be part ofrounded-trapezoidal cutouts having a shape that is a portion of atrapezoid having rounded corners. The sloped surfaces of ramps 162, 164,262, 264 may be substantially parallel to the sloped surfaces ofoverhanging guides guide 372, 374, 376, 378 of the endplates 300 thatare located near them. There may be corresponding sloped features on anendplate 300 as described elsewhere herein. It is possible that at themaximally vertically contracted configuration of the device 10, theoverhanging guides guide 372, 374, 376, 378 can bottom out against theramps or cutouts 162, 164, 262, 264.

It is possible that at the maximally vertically contracted configurationof the device 10, a stability bar 370 from the upper endplate 300 canbottom out against the stability bar 370 from the lower endplate 300.

The inside width between the overhanging guides 362, 364 that arelaterally opposite each other can be chosen to be approximately equal tothe larger inside width of the appropriate one of the ring structureswith which that overhanging guide interacts. The external width of theoverhanging guides that are laterally opposite each other can be chosento be approximately equal to the larger external width of theappropriate one of the ring structures with which that overhanging guideinteracts. Both of these dimensional choices would help to align therespective ramp or bearing surfaces with each other for load transferbetween the overhanging guides and the appropriate ring structure. Theoverhanging guides may slide on the corresponding slide ramps such as162, 164 of the proximal ring structure 100 or side ramps 262, 264 ofthe distal ring structure 200.

The external width of the overhanging guides that are laterally oppositeeach other can be chosen to be substantially equal to the external widthof the endplate 300 at that same location, which may also be at leastapproximately equal to the maximum external width PEW1 of the proximalring structure 100 or the maximum external width DEW1 of the distal ringstructure 200.

The slopes of the rounded-trapezoidal receiving cutout may have slopesthat match the slopes of the angles of the sides of the trapezoidaloverhanging guide 372, 374, 376, 378.

It is possible, as illustrated, that the endplate 300 may have both astability bar 370 more internally and an overhanging guide 372, 374,376, 378 more externally, with relatively internal and relativelyexternal being defined in the lateral direction.

Referring now to FIG. 11 and FIG. 12, it is possible that thetranslational motion is driven by an actuation mechanism 400 and isguided by a guide mechanism 500 different from the actuation mechanism400, with the actuation mechanism 400 being located at a first end ofthe device 10 and the guide mechanism 500 being located at a secondopposed end of the device 10. The actuation mechanism 400 may have anactuation axis and the guide mechanism 500 may have a guide axis, andthe actuation axis and the guide axis may be collinear with each other.The actuation mechanism 400 may be at the proximal end of the device 10,and the guide mechanism 500 may be at the distal end of the device 10.

An embodiment of the invention may comprise actuation mechanism 400which may comprise drivescrew 450. As illustrated, the drivescrew 450may have threaded engagement with hole 280 in distal ring structure 200.Accordingly, drivescrew 450 may have a threaded region 452 of drivescrew450. As illustrated, drivescrew 450 may have a simple pass-throughrelationship (i.e., no thread engagement) with hole 180 in proximal ringstructure 100, which may be achieved with drivescrew 450 having anunthreaded region 454 adjacent to its head 460, although other designsare possible also. Drivescrew 450 may have an enlarged head 460 thatbears against recess 182 in proximal ring structure 100 to transmitforce and serve as a stop against translational motion in one directionof drivescrew 450 relative to proximal ring structure 100. Thus, whendrivescrew 450 is rotated in the appropriate direction, it may pulldistal ring structure 200 in a translational manner toward proximal ringstructure 100, or more specifically may pull first side 221 of distalring structure 200 toward first side 121 of proximal ring structure 100.This may accomplish vertical expansion of the overall device 10. It isfurther possible that when drivescrew 450 is rotated in the appropriateopposite direction, drivescrew 450 may push first side 221 of distalring structure 200 away from first side 121 of proximal ring structure100. This may accomplish vertical contraction of the device 10. Thismotion may be assisted by the capture of snap-ring 490 in both groove480 of drivescrew 450 and groove 196 of proximal ring structure 100.Such captured relationship may provide reaction force to preventexpulsion of the drivescrew 450 from proximal ring structure 100 duringvertical contraction of the overall device 10.

Drivescrew 450 may additionally have a tool interface feature such as anon-circular socket, suitable to engage a feature of a tool and receivetorque from the tool. Of course, other designs of drive mechanism 400are also possible.

Referring now to FIG. 14D, an embodiment of the invention may furthercomprise a guide mechanism 500. Guide mechanism 500 may be located atthe opposite end of the device, along the longitudinal direction, fromthe end where the actuation mechanism 400 is located. Guide mechanism500 may comprise a guide pin 590 that may be fixedly attached to one ofthe ring structures 100, 200, and may be in slidable relationship withthe other of the ring structures 100, 200. In such manner, translationalmotion is allowed between proximal ring structure 100 and distal ringstructure 200 along the longitudinal direction, but constraint isprovided against certain other forms of motion. More specifically, asillustrated, guide pin 590 is in slidable relationship with hole 190 inproximal ring structure 100. Also as illustrated, guide pin 590 is infixed relationship with distal ring structure 200. As illustrated, guidepin 590 may be externally threaded and hole 290 in distal ring structure200 may be internally threaded to accept the threads of guide pin 590.However, it is possible that the threadedness of hole 290 and theslidable relation of hole 190 could be reversed. It is also to beunderstood that other designs, such as press-fitted relationship orstaked relationship, are also possible. It can also be noted that it isnot essential for there to be any guide mechanism 500 at all.

It can be noted that the central opening 12 of the device 10 does nothave a drivescrew or any other component crossing entirely across thecentral opening 12 in the longitudinal direction or any direction, andso central opening 12 can provide a relatively unobstructed path for thepacking of bone growth promoting material in the central opening 12 andfor the growth of bone through the central opening 12. This is true forthe entire permitted range of positions of the proximal ring structure100 relative to the distal ring structure 200, and for the entirepermitted range of positions of upper endplate 300 relative to lowerendplate 300. It is possible, depending on design details, that in someconfigurations there may be a modest projection of the actuationmechanism 400 into the central space, or a modest projection of theguide mechanism 500 into the central space, and in some configurationsthere may be no projection at all of one or the other of the actuationmechanism 400 and the guide mechanism 500. It can be seen that in anyconfiguration, there is not a component that traverses all the wayacross the central opening 20 in the longitudinal direction or anydirection. Although it should be understood that a component maytraverse all the way across the central opening 20 in the longitudinaldirection or any direction.

It is possible that, when the device 10 is in its minimum-heightconfiguration, the urging structure 250 may extend less far in thevertically outward direction than the extreme ends of the teeth orsimilar features of the surface 302 endplate 300 extend in thevertically outward direction. It is possible that one surface of theurging structure 250 may have a slope that is approximately equal to oneof the slopes of the grooves or ridges on the bone-facing surface of theendplate 300, i.e., the slope of the urging structure 250 mayapproximately equal either the slope of the leading edge or the slope ofthe trailing edge of the ridge or groove.

The interaction and force generation and motion generation between theproximal ring structure 100 and the driven ring structure may come froma drivescrew 450 that engages both the driving ring structure and thedistal ring structure 200 without crossing the graft region in theforward-backward direction. The drivescrew 450 may be at the end of theassembly that is opposite the nose 115 of the assembly. The nose 115 maybe a feature that is tapered, pointed or otherwise configured to pushtissue out of its way to facility entry of the assembly into a surgicalsite.

Driving motion may be provided by a drivescrew 450 that is threadinglyengaged with one ring structure and rotatably engaged with the otherring structure, both at a particular end of the assembly on a particularside of the graft window. Motion may be carried around the graft windowspace by the ring nature of the proximal ring structure 100 and distalring structure 200. There may be a driven ramp and there may be a ringstructure vertical extension that interacts with a feature of theendplate to urge the endplate ramp along the corresponding ramp in thedriving ring structure.

Contracting of the assembly may also be driven by the drivescrew withthe drivescrew being rotated in the direction of rotation opposite ofthe direction that caused expansion. Such rotation of the drivescrew maycause the vertical extension of the driven ring structure to pushagainst a feature of the endplate to urge the endplate to slide alongthe ramps in a direction that results in contracture of the assembly inthe intervertebral longitudinal direction.

Among the driving ring structure and the driven ring structure, all ofthe ramps that interact with an endplate may be located on one of thering structures, which, for discussion purposes here, may be the drivingring structure. There may be two ramp interactions between the drivingring structure and any given endplate. One such ramp interaction may becloser to the forward end of the assembly and the other such interactionmay be closer to the rearward end of the assembly. Both ramps may haveengagement features which may be captured features such as a T-slot anda complementary shape, thereby allowing the endplate to be in a capturedconfiguration with respect to the central mechanism. One of the rampinteractions may be such that the proximal ring structure 200 has thereceiver while the endplate 300 has the protrusion. The other rampinteraction may be such that the proximal ring structure 200 has theprotrusion and the endplate 300 has the receiver. As illustrated, a rampwith a receiver is on the proximal ring structure 200 close to theproximal end of the device 10. A ramp with a projection is on theproximal ring structure 200 towards the distal end of the device 10.Opposite features are on the endplate 300. As illustrated, theprojection is a T-shape and the receiver is a T-shaped groove, althoughother geometries (either capturing or non-capturing) are possible.

Given that the assembly can both expand and contract, expansion may bedriven by a vertical (or nearly vertical) surface of the urgingstructure 250 bearing against a vertical (or nearly vertical) surface ofthe endplate, which may be an internal surface of an opening 310 throughendplate 300, and contraction may be driven by a vertical surface of theurging structure 250 bearing against a vertical surface of a stabilitybar 370. More generally, in this situation, “vertical” may mean avertical or nearly-vertical surface.

The driven ring structure may comprise an urging structure 250, whichmay be driven by the drivescrew and may in turn interact with theendplate so as to urge the endplate to move in a horizontal directionwith respect to the driving ring structure, thereby resulting invertical motion of the endplate in view of the slope of the ramp. Theurging structure 250 may be capable of interacting with the endplate intwo different ways. One surface of the urging structure 250 may interactwith a corresponding surface of the endplate such as an internal surfaceof an opening 310 through the endplate 300 so as to drive the endplatein expansion, and another surface of the urging structure 250 mayinteract with another corresponding surface of the endplate, in thiscase the stability bar 370, so as to drive the endplate in contraction.It may be appreciated that, in order that the endplate 300 and itsstability bars 370 be able to translate vertically, the near-end wallthickness of the urging structure 250, in the longitudinal direction,may be equal to or just slightly less than the distance, in alongitudinal direction, between the vertical surface of the centralopening 310 of endplate 300 and the nearby vertical surface of astability bar 370.

A graft window may be defined at least in part by an end surface of theproximal ring structure 100, an end surface of the distal ring structure200, and the inwardly-facing surfaces of the pair of stability bars 370of each endplate 300.

It is possible that in the fully collapsed configuration, the ends ofthe stability bars 370 of one endplate 300 may touch the correspondingends of the stability bars 370 of the other endplate 300.

It can be observed that there may be provided an implantable device 10having a central mechanism comprising a first structure and a secondstructure able to undergo relative translation with respect to eachother, with at least one of the structures having a driving ramp havingan interlocking feature, and comprising an endplate 300 having anendplate ramp complementary to the driving ramp and to its interlockingfeature, and comprising a drive means 400, wherein translation of thecentral mechanism in one direction drives the endplate 300 away from thecentral mechanism and translation of the central mechanism in theopposite direction drives the endplate 300 toward the central mechanism,and wherein the central mechanism has a central opening therethrough andthe drive means 400 does not cross the central opening 12.

FIG. 12 illustrates that the drive means 400 may protrude to some extentinto the central opening 12 of device 10, while still leaving most ofcentral opening 12 unobstructed. It is possible that when device 10 isin a vertically expanded configuration, drive means 400 may protrudefurther into central opening 12 than is true for the verticallycontracted configuration. It is possible that such increased protrusionof drive means 400 can help urge graft material to reconfigure itselfand contact adjacent vertebrae.

FIGS. 13A-13B illustrate possible load paths when the device 10 is beingexpanded. FIGS. 13A-13B illustrate that redundant load paths may beprovided. FIG. 13A is a section taken at the centerplane, and FIG. 13Bis a section taken at a plane removed from the centerplane. Asillustrated in the load path labeled load path 1, drivescrew 450 mayinteract with urging structure 250, which may be part of first side 221of distal ring structure 200, to generate motion or load, which may betransmitted to and through urging structure 250 such that urgingstructure 250 contacts the facing surface of endplate 300 and therebyurges endplate 300 to slide along the appropriate ramp surfaces, ofproximal ring structure 100. Such motion advances endplate 300 leftward(as illustrated) with respect to proximal ring structure 100, andthereby advances endplate 300 vertically away from proximal ringstructure 100 and distal ring structure 200. Also present in the device10 is another possible load path, labeled load path 2. In load path 2,load may be generated by the interaction of drivescrew 450 with distalring structure 200 specifically first side 221 of distal ring structure200, and that load may be transmitted along the length of distal ringstructure 200 via sides 222, 224 to the (distal) third side 223 ofdistal ring structure 200, such that a distal urging surface of distalring structure 200 contacts a distal surface of endplate 300 and urgesendplate 300 to slide along appropriate ramp surfaces (131, 132) ofproximal ring structure 100. Such motion also advances endplate 300leftward (as illustrated) with respect to proximal ring structure 100,and thereby advances endplate 300 longitudinally. Thus, two separateinstances or load paths for urging have just been described. It ispossible that both of these load paths may be simultaneously active.However, it is also possible that depending on detailed dimensional andgeometric relationships and tolerances, only one of these described loadpaths may be active. If only one of these load paths is active, it canbe either of the described load paths, again depending on appropriatedimensions and tolerances.

FIGS. 13C-13D also illustrates possible load paths when the device 10 isbeing vertically contracted. FIG. 13C is a section taken at thecenterplane, and FIG. 13D is a section taken at a plane removed from thecenterplane. As illustrated in the load path labeled load path 3,drivescrew 450 may interact with urging structure 250, which may be partof distal ring structure 200, to generate motion or load, which may betransmitted to and through urging structure 250 such that urgingstructure 250 contacts the facing surface of stabilizing bar 370 andthereby urges endplate 300, specifically one or more of its ramps, toslide along the corresponding ramp surface of proximal ring structure100. Such motion advances endplate 300 rightward (as illustrated) withrespect to proximal ring structure 100, and thereby advances endplate300 so as to vertically contract the device 10. The relevant dimensionsof stabilizing bar 370 and urging structure 250 may be such that contactbetween stabilizing bar 370 and urging structure 250 is maintained overthe desired range of motion.

It is further possible that proximal ring structure 100 and distal ringstructure 200 and both the drive means 400 and the guide means 500 mayhave respective central holes therethrough along the longitudinaldirection of the device 10. These holes may be suitable to receivetherein a guidewire such as a K-wire (Kirschner wire).

Anti-Back-Out Features or Locking Features

Optionally, an embodiment of the invention may comprise a feature toresist, limit or prevent backout or disassembly in regard to thedrivescrew. Such feature either may resist rotation of the drivescrew450 in both directions of rotation, or may preferentially resistrotation of the drivescrew 450 in the direction that corresponds todecrease of height of the overall device 10.

Drivescrew 450 may comprise a threaded shaft that engages acorresponding thread in distal ring structure 200. Referring now toFIGS. 14A-14C, drivescrew 450 may comprise a deformable member 463,which may be or may comprise a polymer that is softer than the materialof which the drivescrew 450 is made. (Drivescrew 450 may be made ofmetal such as titanium or a titanium alloy.) Deformable member 463 maybe placed and dimensioned to bear against a corresponding feature ofproximal ring structure 100 in such a way as to create friction andresist motion of the drivescrew 450 with respect to proximal ringstructure 100. Such deformable member 463 may initially be oversized sothat it occupies larger space than the remaining threads of drivescrew450 and creates a slight interference with the complementary threadsthat drivescrew 450 engages in distal ring structure 200. Thisinterference may result in friction that resists rotation of drivescrew450 with respect to distal ring structure 200. The deformable member 463also may have damping or vibration absorption properties. Asillustrated, deformable member 463 is placed in a receiving feature thatis a slot 462 that passes through the threaded shaft 452 of drivescrew450, although other geometries are also possible for placement ofdeformable member 463 in drivescrew 450.

It is further possible that the head of drivescrew 450 may contain adrivescrew groove 480 suitable to receive a snap-ring 490. Thedrivescrew groove in the head of drivescrew 450 may be axisymmetric.When the snap-ring 490 is in an unstrained state and is assembled so asto overlap with drivescrew groove 480, part of snap-ring 490 may becontained within drivescrew groove 480 and some other part of snap-ring490 may extend out beyond drivescrew groove 480.

Proximal ring structure 100 may contain a proximal ring structure groove196 that is dimensioned suitably to receive a portion of snap-ring 490.

Snap-ring 490 may further comprise a rounded leading outer edge, and maycomprise a relatively sharp-cornered trailing outer edge. Proximal ringstructure 100 may comprise an entrance chamfer, and proximal ringstructure groove may comprise at least some sharp corners. Such featureshave been described in U.S. Pat. Nos. 7,001,389 and 7,766,911 and7,780,666 and 7,785,327, which are hereby incorporated by reference intheir entirety.

It is possible that snap-ring 490 and deformable member 463 may be usedtogether in the same drivescrew 450. Alternatively, it is possible thateither one of them could be used separately.

It is possible that the thread on the drivescrew 450 could, incross-section in a plane that contains the longitudinal axis ofdrivescrew 450, have a thread profile having a leading edge angle and atrailing edge angle that are different from each other. It is possiblethat the leading edge or the trailing edge could, in that samecross-section, be substantially perpendicular to the longitudinal axisof drivescrew 450.

It is possible that in an embodiment of the invention, there may beprovided an implantable device having a central mechanism comprising afirst structure and a second structure, wherein the first structure andthe second structure are connected by a drive means comprising adrivescrew, wherein the drivescrew comprises a head groove and one ofthe structures comprises a circumferential internal groove, and furthercomprising a snap-ring that partially occupies the head groove andpartially occupies the circumferential internal groove. The partialoccupying of the head groove and partial occupies the circumferentialinternal groove may occur at an unstrained configuration of thesnap-ring.

General Considerations

Proximal ring structure 100, distal ring structure 200 and generallymost other components may be made of a biocompatible metal such astitanium or a titanium alloy. However, endplates 300 may be made of ormay comprise a polymer such as polyetheretherketone (PEEK). Anycomponents may have appropriate coatings or surface treatments. Forexample, outward-facing surfaces may have a coating or surface treatmentto encourage bone ingrowth. Sliding surfaces may have afriction-reducing coating or surface treatment.

In regard to assembling the described device 10, it is possible thatfirst the proximal ring structure 100 may be assembled together with thedistal ring structure 200, together with connecting components such asdrive mechanism 400 and guide mechanism 500 (if used). Then, the drivemechanism 400 can be used to configure the assembly in a configurationcorresponding to maximum or nearly maximum vertical expansion of thedevice, if the endplates 300 were present. Then, the endplates 300 canbe slid onto the corresponding ramps of proximal ring structure 100 orany other relevant structure. Then, the drive mechanism can be used toreconfigure the assembly to a less than fully vertically expandedconfiguration, or perhaps to a fully vertically contracted configurationsuch as may be used for insertion of the device into a patient.

A possible typical vertical dimension of the device 10 may be a verticalheight of 8 mm in the vertically contracted configuration, and avertical height of 12 mm in the vertically expanded configuration. Thismeans that the upper endplate 300 would have the ability to move 2 mmaway from the central mechanism compared to its closest position, andthe lower endplate 300 would also have the ability to move 2 mm awayfrom the central mechanism compared to its closest position. If thevarious ramps have a slope of 45 degrees, this means that there wouldhave to be a corresponding 2 mm of horizontal motion of and endplateramp with respect to a ramp on the proximal ring structure 100. For thedescribed design, this also implies 2 mm of relative horizontaltranslation of the proximal ring structure 100 and the distal ringstructure 200. For example, the device 10 could have an overall lengthin the longitudinal direction of 24 mm when vertically contracted, andan overall length in the longitudinal direction of 22 mm when verticallyexpanded. Of course, devices having other dimensions are possible, andproviding a set or kit containing various sizes of devices is alsopossible.

FIG. 15A is a three-dimensional illustration of two devices of anembodiment of the invention, placed in an intervertebral disc space,viewed from the anterior, with one vertebra shown semi-transparent, andwith the intervertebral disc omitted for clarity of illustration.

FIG. 15B is a three-dimensional illustration of two devices of anembodiment of the invention, placed in an intervertebral disc space,viewed from the posterior, with one vertebra and the intervertebral discomitted for clarity of illustration.

FIG. 15C is similar to FIG. 15B, with one vertebra and theintervertebral disc omitted for clarity of illustration, but with onlyone device shown, and further showing a portion of an implantationinstrument.

During surgery, the device 10 may be introduced into the patient's bodyin a vertically contracted configuration and then may be reconfigured toa vertically expanded configuration. At some appropriate time thecentral opening 12 may be packed with bone growth promoting material asknown in the art.

It is also possible that an embodiment of the invention could haveendplates 300 that have only one overhang per side, rather than twooverhangs per side as has been illustrated. The overhangs in such anembodiment still may have ramps as described, that interact with rampson proximal ring structure 100 or distal ring structure 200 or both.

While several inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

All documents referred to herein are incorporated by reference in theirentirety. The following US publications are incorporated by reference intheir entirety: 20100211176; 20100222884; 20070219634.

We claim:
 1. A spinal interbody device, comprising: a proximal ringstructure having a proximal ring structure opening therethrough, saidproximal ring structure opening having a proximal ring structure openingdirection; a distal ring structure having a distal ring structureopening therethrough; an actuation mechanism suitable to cause relativemotion between said proximal ring structure and said distal ringstructure along a longitudinal axis, said relative motion including atleast relative translation along a first motion direction along saidlongitudinal axis, wherein, at any permitted relative position of saidproximal ring structure and said distal ring structure, when viewedalong said proximal ring structure opening direction, said proximal ringstructure opening and said distal ring structure opening partially butnot completely overlap with each other; a first endplate and a secondendplate, wherein said first endplate and said second endplate areopposed to each other and are suitable to bear against respectivevertebrae; wherein said relative motion between said proximal ringstructure and said distal ring structure causes at least one of saidfirst endplate and said second endplate to move toward or away from saidproximal ring structure or said distal ring structure in a second motiondirection different from said first motion direction.
 2. The spinal bodyimplant of claim 1, wherein said proximal ring structure includes aproximal end and a distal end, wherein said proximal ring structureopening decreases in width along said longitudinal axis from saidproximal end towards said distal end.
 3. The spinal body implant ofclaim 2, wherein said distal ring structure includes a proximal end anda distal end, wherein said distal ring structure opening decreases inwidth along said longitudinal axis from said proximal end towards saiddistal end.
 4. The spinal body implant of claim 3, wherein there is asequence progressing along said longitudinal axis said proximal end ofsaid distal ring structure followed by said distal end of said proximalring structure followed by said distal end of said distal ring structurefollowed by said proximal end of said proximal ring structure.
 5. Thespinal body implant of claim 3, wherein a first external width of saidproximal end of each said proximal ring structure and said distal ringstructure is larger than a second external width of said distal end ofeach said proximal ring structure and said distal ring structure.
 6. Thespinal body implant of claim 3, wherein said actuation mechanismconnects said distal end of said distal ring structure to said proximalend of said proximal ring structure.
 7. An implantable device,comprising: a proximal ring structure having a proximal ring structureopening therethrough and a proximal end and an opposing distal end; adistal ring structure having a distal ring structure openingtherethrough and a proximal end and an opposing distal end, wherein saiddistal ring structure being in movable relation to said proximal ringstructure, said movable relation including at least translation in afirst direction along a longitudinal axis; wherein said proximal ringstructure and said distal ring structure define an open regiontherethrough perpendicular to said first direction; a first endplate,said first endplate having a face suitable to bear against a vertebra,said face having a central opening therethrough in communication withsaid open region; said device includes a proximal end and an opposingdistal end, wherein said open region is between said proximal end andsaid opposing distal end, wherein said device proximal end includes saidproximal ring structure proximal end and said distal ring structuredistal end and said device distal end includes said proximal ringstructure distal end and said distal ring structure proximal end; and anactuation mechanism connecting said proximal ring structure proximal endto said distal ring structure distal end, wherein said translation ofsaid proximal ring structure relative to said distal ring structure insaid first direction causes motion of said first endplate away from saidproximal ring structure, and translation of said proximal ring structurerelative to said distal ring structure in a second direction opposed tosaid first direction causes said first endplate to move toward saidproximal ring structure.
 8. The implantable device of claim 7, whereinsaid actuation mechanism does not cross said open region into saidproximal ring structure distal end and said distal ring structureproximal end.
 9. The implantable device of claim 7, wherein said openregion increases in length along said longitudinal axis when saidtranslation of said proximal ring structure relative to said distal ringstructure in said first direction causes motion of said first endplateaway from said proximal ring structure.
 10. The implantable device ofclaim 9, wherein said open region decreases in length along saidlongitudinal axis when said translation of said proximal ring structurerelative to said distal ring structure in said second direction opposedto said first direction causes said first endplate to move toward saidproximal ring structure.
 11. The implantable device of claim 7, whereinthere is a sequence progressing along said longitudinal axis saidproximal end of said distal ring structure followed by said distal endof said proximal ring structure followed by said open region followed bysaid distal end of said distal ring structure followed by said proximalend of said proximal ring structure.
 12. The implantable device of claim7, further comprising a second endplate, wherein said first endplate andsaid second endplate are opposed to each other and each are suitable tobear against respective vertebrae.
 13. A surgical kit comprising: atleast one spinal interbody device, comprising: a proximal ring structurehaving a proximal ring structure opening therethrough, said proximalring structure opening having a proximal ring structure openingdirection; a distal ring structure having a distal ring structureopening therethrough; an actuation mechanism suitable to cause relativemotion between said proximal ring structure and said distal ringstructure along a longitudinal axis, said relative motion including atleast relative translation along a first motion direction along saidlongitudinal axis, wherein, at any permitted relative position of saidproximal ring structure and said distal ring structure, when viewedalong said proximal ring structure opening direction, said proximal ringstructure opening and said distal ring structure opening partially butnot completely overlap with each other; a first endplate and a secondendplate, wherein said first endplate and said second endplate areopposed to each other and are suitable to bear against respectivevertebrae; wherein said relative motion between said proximal ringstructure and said distal ring structure causes at least one of saidfirst and second endplates to move toward or away from said proximalring structure or said distal ring structure in a second motiondirection different from said first motion direction, and wherein saiddevice has a central opening therethrough generally along a verticaldirection, said central opening being bounded in sequence around itsperimeter by a first end, a first side, a second end and a second side,wherein in said sequence, said central opening is bounded on said firstend by said proximal ring structure; then, on said first side adjacentto said first end, said central opening is bounded first by saidproximal ring structure and then is bounded by said distal ringstructure; then, on said second end, said central opening is bounded bysaid distal ring structure; then, on said second side, said centralopening is bounded first by said distal ring structure and then by saidproximal ring structure.
 14. The surgical kit of claim 13, furthercomprising a surgical instrument to grasp said at least one spinalinterbody device.
 15. The surgical kit of claim 13, further comprising asecond spinal interbody device different in dimension from said at leastone spinal interbody device.
 16. The surgical kit of claim 13, whereinsaid central opening may be packed with bone growth.